Photochromic organic materials

ABSTRACT

The invention relates to photochromic transparent organic materials presenting an index of refraction of more than 1.55, which are free of optical distortions and are prepared by radical polymerization of a polymerizable composition comprising: 
     a) 80-95 wt % of at least one monomer represented by the general formula (I): ##STR1##  where R=H or CH 3 , and m and n are independently 1 or 2; b) 5-20 wt % of at least one aromatic monovinyl monomer represented by the general formula (II): ##STR2## c) an effective quantity of at least one dye that imparts photochromic properties to the material, selected from the groups of spiroxazines, spiropyrans and chromenes; 
     d) an effective quantity of a chain transfer agent; and 
     e) an effective quantity of a radical polymerization initiator, characterized in that the chain transfer agent is a linear alkanethiol and the radical polymerization initiator is a diazo compound.

BACKGROUND OF THE INVENTION

The invention relates to novel photochromic transparent organicmaterials with high index of refraction presenting no optical distortionin solid form, a method for their preparation, and the articles madefrom these materials.

It is difficult to prepare such a photochromic ophthalmic lens made ofplastic material. Ideally, the polymer matrix of such a lens should becrosslinked thermally, free of optical distortion in solid form and ableto receive appropriate mixtures of photochromic dyes and to becrosslinked in the presence of such appropriate mixtures of photochromicdyes, for example spiroxazines and chromenes, to obtain a material whichpresents a high initial transmission before exposure and a high capacityfor darkening after exposure, all with rapid darkening and lighteningkinetics. In addition, the material should have a low thermaldependence, a high resistance to fatigue, and as high an index ofrefraction as possible.

Obviously, no such ideal material exists to date.

WO-A-92/05209 describes a copolymer that is free of optical distortionsand is suitable for the manufacture of eyeglasses, and is obtained by aradical polymerization of a first monomer with formula I ##STR3## wherea and b are whole numbers from 0 to 4, R₁ and R₂ =H or CH₃, and R₃=--O--, --S--, --CO--, --SO₂ --, --CH₂ --, --CH═CH-- or ##STR4## with asecond monomer, which can be styrene or a styrene derivative an,optionally, a third monomer, which can be a vinyl aromatic compound oran aromatic methacrylate, in the presence of an initiator of theperoxide type and of a chain transfer agent selected from variousbrominated compounds.

This copolymer could be a good polymer matrix for an ophthalmic article,such as a lens.

However, when one tries to incorporate ophthalmic dyes in thecopolymerizable composition to impart ophthalmic properties to thematrix obtained after copolymerization, it can be observed that saiddyes are destroyed by the peroxide initiator.

Even if the peroxide initiator is replaced by a milder radicalpolymerization initiator, such as a diazo compound, for example,azobisisobutyronitrile, the material obtained is still unsatisfactory,because the photochromic dyes are inhibited by the bronninated chaintransfer agent used, as has been observed by the present inventors. Itis also necessary to later incorporate the dyes into the matrix notablyby a specific thermal diffusion method, which increases the cost priceof the material and complicates its manufacturing process.

Thus, there is a need for high-performance ophthalmic materials that areeasy and inexpensive to manufacture.

The present invention is intended to meet this need.

SUMMARY OF THE INVENTION

More particularly, the present invention concerns novel ophthalmictransparent organic materials presenting an index of refraction of morethan 1.55, which are free of optical distortions and are prepared byradical polymerization of a polymerizable composition comprising:

a) 80-95 wt % of at least one monomer represented by the general formula(I): ##STR5## where R=H or CH₃, and m and n are independently 1 or 2; b)5-20 wt % of at least one aromatic monovinyl monomer represented by thegeneral formula (II): ##STR6## where R₁ =H or CH₃ c) an effectivequantity of at least one dye that imparts photochromic properties to thematerial, selected from the groups of spiroxazines, spiropyrans andchromenes;

d) an effective quantity of a chain transfer agent; and

e) an effective quantity of a radical polymerization initiator;

characterized in that the chain transfer agent is a linear alkanethioland the radical polymerization initiator is a diazo compound.

Optionally, the polymerizable composition can contain, in addition, f)up to 10 wt % of an aromatic divinyl monomer represented by the generalformula (III): ##STR7## where R₁ =H or CH₃.

The invention also relates to a method for the preparation of novelphotochromic transparent organic materials presenting an index ofrefraction of more than 1.55, which are free of optical distortions,characterized in that it consists of carrying out a radicalpolymerization of a polymerizable composition comprising:

a) 80-95 wt % of at least one monomer represented by the general formula(I): ##STR8## where R=H or CH₃, and m and n are, independently, 1 or 2;b) 5-20 wt % of at least one aromatic monovinyl monomer represented bythe general formula (II): ##STR9## c) an effective quantity of at leastone dye that imparts photochromic properties to the material, selectedfrom the groups of spiroxazines, spiropyrans and chromenes;

d) an effective quantity of a chain transfer agent; and

e) an effective quantity of a radical polymerization initiator.

Optionally, it is also possible that in the polymerizable compositioncan contain, in addition.

f) up to 10 wt % of an aromatic divinyl monomer represented by thegeneral formula (III): ##STR10## where R₁ =H or CH₃.

The monomers (a) with formula I are well known and commerciallyavailable. For example, a monomer with formula I where R=H and m and n=2is marketed by the company Akzo under the trade name Diacryl 121.Styrene and methylstyrene are the monomers (b) with formula II. Themonomers (f) with formula III are represented by divinylbenzene anddi(methylvinyl)benzene.

By an appropriate selection of the monomers (a), (b) and (f) and theirproportions, the kinetic parameters of the final photochromic material(darkening rate, bleaching rate) can be adjusted as desired: theaddition of a monomer (b) such as styrene to the dimethacrylic compound(a), besides having an advantageous effect on the optical properties,also reduces the kinetics of the dyes that would intrinsically be toorapid in the methacrylic matrix. Conversely, the optional incorporationof a third monomer (f), such as divinylbenzene, on the contrary allowsthe acceleration of a dye that would be too slow in the methacrylicmatrix. Thus, by a careful selection of the ratio by weight of monomer(b):optional monomer (f), it is possible in a dimethacrylic matrix suchas the one described to adjust the kinetic parameters of thephotochromic process to a desired value without altering the opticalquality of the materials obtained and while preserving a high index ofrefraction.

The photochromic dye (c) can be selected from the general classes ofspiroxazines, spiropyrans and chromenes with photochromic propertiesimparted. A very large number of photochromic dyes of this type havebeen described in the literature and are commercially available. Usablespiroxazine dyes have been described notably in U.S. Pat. Nos.3,562,172, 4,634,767, 4,637,698, 4,720,547, 4,756,973, 4,785,097,4,792,224, 4,816,584, 4,831,142, 4,909,963, 4,931,219, 4,936,995,4,986,934, 5,114,621, 5,139,707, 5,233,038, 4,215,010, 4,342,668,4,699,473, 4,851,530, 4,913,544, 5,171,636, 5,180,524, 5,166,345 and inEP-A 0,508,219, 0,232,295, and 0,171,909, among others. Usable chromeneshave been described in U.S. Pat. Nos. 567,605, 4,889,413, 4,931,221,5,200,116, 5,066,818, 5,244,602, 5,238,981, 5,106,998, 4,980,089,5,130,058, and in EP-A 0,562,915, among others. Useful spiropyrans havealso been described in the following general works:

Photochromism, G. Brown, Editor, Techniques of Chemistry, WileyInterscience, Vol. III, 1971, Chapter III. pages 45-294, R. C.Bertelson.

Photochromism, Molecules & Systems, Edited by H. Durr, H. Bouas-Laurent,Elsevier 1990, Chapter 8: Spiropyrans, pages 314-455, R. Guglielmetti.

The teachings of all these patents and documents are incorporated hereby reference.

As a nonlimiting indication, the proportion of the photochromic dyes tobe incorporated in the polymerizable composition can range from 0.01 to1.0 wt %, preferably 0.05-0.5 wt %, with respect to the weight of themonomers.

It is also preferred to use a combination of photochromic dyes whichimpart a gray or brown tint in the darkened state.

The chain transfer agent (d) is selected from the C₂ -C₁₆ linearalkanethiols. Linear C₄ -C₁₆ alkanethiols are preferred, because theyare less volatile than the C₂ or C₃ homologs. Specific examples are:butanethiol, pentanethiol, hexanethiol, heptanethiol, octanethiol,decanethiol, dodecanethiol and tetradecanethiol. Purely as anindication, the chain transfer agent can be incorporated in thepolymerizable composition in a proportion of 100-5,000 ppm, for example,with respect to the monomers. Another product which we have found to beuseful both as a chain transfer agent and as a chain extender isbis-mercapoethyl ether (MEE) having the general formula:

    HS--CH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.2 --SH.

The radical polymerization initiator (e) is selected from the diazoinitiator.

These compounds are well known and available commercially. Specificexamples are azobisisobutyronitrile (AIBN) and2,2'-azobis(2-methylbutyronitrile) (AMBN), among others. Purely as anindication, a proportion of initiator equivalent to about 0.05-0.5 wt %of the monomers can be incorporated in it.

The joint use of an alkanethiol as ingredient (d) and a diazo compoundas ingredient (e) allows the obtention of the advantages procured by theinvention, that is, the possibility of preparing a photochromic materialwith excellent properties by a radical polymerization in the presence ofat least one photochromic dye.

The invention concerns the articles made in their entirety or in part ofan organic photochromic material according to the invention.Nonlimniting examples of such articles are ophthalmic corrective lenses,sun-protection lenses, window glass for vehicles or buildings, etc. Inthese articles, the photochromic material of the invention can comprisethe entire thickness of the article (solid article), or it can be in theform of a film or a stratified layer applied to a transparent or mineralsupport.

The ophthalmic lenses are the preferred articles, and they can beproduced conveniently by carrying out the polymerization in lens molds,for example, as described in U.S. Pat. Nos. 2,242,386, 3,136,000 or3,881,683.

In order to explain the invention clearly, the following nonlimitingexamples are given. All the proportions indicated are parts by weight.In all the examples, the polymerization of the polymerizable compositionis conducted in a lens mold under the following conditions: Thepolymerizable composition is heated slowly until the beginning of thethermal degradation of the diazo compound (e) with release of freeradicals. Once the temperature has reached 53° C., it is maintained for16 hours; then, within 3 hours, the temperature is raised to 90° C., andthen maintained for 2 hours. The lens obtained is then removed from themold. The raw materials used in the examples are the following:

    ______________________________________                                        Monomers:                                                                     ______________________________________                                        Diaciyl 121               (DIA)                                                 (available from Akzo Chemical)                                                Styrene (STY)                                                                 Divinylbenzene (DVB)                                                          α-Methylstyrene (MST)                                                   Catalysts:                                                                    2,2'-Azobis-2-methylbutyronitrile (AMBN)                                      Azobisisobutyronitrile (AIBN)                                                 Chain transfer agent:                                                         Dodecanethiol (according to the invention) (DDT)                              Tetrabromomethane (comparative example) (TBM)                                 Bis-mercapoethyl ether (MEE)                                                Photochromic dyes:                                                                Name       Manufacturer     Chemical type                                   Blue D (Great Lakes) Spiroxazine                                              Red PNO (Great Lakes) Spiroxazine                                             Yellow L (Great Lakes) Chromene                                               Sea Green (James Robinson Ltd.) Spiroxazine                                   Berry Red (James Robinson Ltd.) Chromene                                    ______________________________________                                    

EXAMPLES 1-8

Examples 1-8 show the efficacy of the chain transfer agents (DDT) and(MEE) in eliminating optical distortions (For this purpose only, theexamples are provided in polymerizable compositions without photochromicdye).

    __________________________________________________________________________               Chain                                                                 Monomers (g) Transfer Agent (g) Catalyst Appearance                        Ex                                                                              DIA                                                                              STY                                                                              DVB                                                                              DDT                                                                              TBM                                                                              MEE**                                                                             AMBN (g)                                                                            AIBN (g)                                                                           #     n.sub.d                                 __________________________________________________________________________    1 100                                                                              -- -- -- 0.4                                                                              --  0.2   --   Lg    1.557                                              distortions                                                          2 80 20 -- -- 0.4 -- 0.2 -- distortions 1.565                                 3 80 20 -- 0.4 -- -- 0.2 -- no *                                                       distortions                                                          4 80 10 10 0.4 -- -- 0.2 -- no 1.566                                                   distortions                                                          5 100 -- -- -- -- 0 -- 0.2                                                    6 98 -- -- -- -- 2 -- 0.2                                                     7 96 -- -- -- -- 4 -- 0.2                                                     8 94 -- -- -- -- 6 -- 0.2                                                   __________________________________________________________________________     # Examination in polarized light                                              *not measured                                                                 **works both as a chain transfer agent as well as a chain extender       

The mixtures of examples 5-8 were polymerized in a lens mold using thefollowing schedule:

16 hours at 65° C.

1 hour at 70° C.

1 hour at 80° C.

1 hour at 110° C.

The indices of refraction of the materials of Examples 1, 2 and 4 were,respectively, 1.557, 1.565 and 1.566.

EXAMPLES 9-16

These examples show that inventive chain transfer agents, dodecanethiol(DDT) and Bis-mercapoethyl ether (MEE) do not alter the photochromicproperties of the dyes, in contrast to the tetrabromomethane (TBM) ofthe prior art. The chain transfer agents and the dyes used, as well astheir proportions and the photochromic proportions of the materialobtained, are indicated in the table below.

    ______________________________________                                                                            After                                       Ex- wt. % Before Aging Aging                                                ample TBM    DDT    MEE  Dye     T.sub.o.sup.(1)                                                                    T.sub.D15(2)                                                                        T.sub.o                                                                           T.sub.D15                     ______________________________________                                        9     --     --     --   Blue D (0.2)                                                                          80   11    80  16                              10 -- -- -- Red PNO 80 11 80 14                                                   (0.025)                                                                   11 0.4 -- -- Blue D (0.2) 80 80 -- --                                         12 0.4 -- -- Red PNO 0.3 0.3 -- --                                                (0.025)                                                                   13 -- 0.4 -- Blue D (0.2) 80 11 81 16                                         14 -- 0.4 -- Red PNO 81 10.5 82 13                                                (0.025)                                                                 ______________________________________                                    

In examples 9-14, the polymenrzable composition consisted of Diacryl 121(80 parts), styrene (20 parts) and AMBN (0.2 part).

In example 15, the polymerizable composition consisted of 100 gramsDiacryl 121, 0.2 grams AIBN and no chain transfer agent.

In example 16, the polymerizable composition consisted of 94 gramsDiacryl 121; 0.2 grams of AIBN and 6 grams of MEE.

The 250-hour aging consisted of exposure to a 60,000-lx xenon lamp(λ=560 nm), at 30° C.

T_(o) is the initial transmission of the lens T_(D15) is thetransmission after 15 min of exposure at 20° C. under a xenon lamp(thickness of the sample: 2 mm).

    ______________________________________                                                wt. %              t.sub.1/2 (sec)*                                   Example TBM    DDT    MEE  Dye     Darkening                                                                            Fading                              ______________________________________                                        15      --     --     --   Blue D (0.2)                                                                          8      12                                    16 -- -- 0.6 Blue D (0.2) 14 18                                             ______________________________________                                         *t.sub.1/2 (dark) is the time required to attain 50% darkening, while         t.sub.1/2 (fade) is the time required to attain 50% fading.              

EXAMPLES 17 AND 18

These examples demonstrate that the use of AMBN instead of aconventional organic peroxide does not change the photochromicproperties.

In these examples, the polymerizable composition consisted of 80 partsof Diacryl 121, 20 parts of styrene, 0.4 part of DDT and the quantitiesof initiator and dye indicated in the table below, which also gives thevalues of To and T_(D15).

    ______________________________________                                                Ex    AMBN    Benzoyl Peroxide                                                                        Dye    T.sub.o                                                                           T.sub.D15 *                        ______________________________________                                        Comparative                                                                           17    --      0.4       Sea Green                                                                            86  74                                       0.015                                                                     Inventive 18 0.4 -- Sea Green 86 11                                               0.015                                                                   ______________________________________                                         *at  = 630 nm (absorption wavelength of Sea Green).                      

EXAMPLES 19-23

These examples show that the chain transfer agent (DDT), even if used athigh concentrations, has no harmful effect on the mechanical propertiesof the material obtained, as shown in Examples 19-23. In these examples,the polymerizable composition consisted of 80 parts of Diacryl 121, 20parts of styrene, 0.4 part of AMBN and the percentage of DDT indicatedin the table below, which also gives the Shore D hardness of thematerial obtained. The polymerizable compositions for these exampleswere prepared without any dyes.

    ______________________________________                                               wt %                                                                   Example  DDT         MEE    Shore D Hardness                                  ______________________________________                                        5        --          0      85                                                  6 -- 2.0 85                                                                   7 -- 4.0 84                                                                   8 -- 6.0 82                                                                   19 0 --  86                                                                   20 0.4 -- 87                                                                  21 0.8 -- 87                                                                  22 1.2 -- 86                                                                  23 3.0 -- 86                                                                ______________________________________                                    

EXAMPLES 24-32

These examples are intended to illustrate the effects resulting from thecopolymerization of monomers (b) and possibly (f) with the monomer (a).

With regard to the addition of styrene (STY) or a mixture of STY+DVB tothe Diacryl 121, besides the fact that in all the cases no opticaldistortion is observed, the mechanical properties of the matrix areimproved. Thus, an elevation of the Tg is observed in the case of thestyrene (STY) and of the hardness in the case of STY+DVB. In theseexamples, the polymerizable composition consisted of 0.2 part of AMBNand 0.4 part of DDT, in addition to the ingredients indicated in thetable below which also indicates the Tg (glass transition temperature)and the Shore D hardness of the material obtained.

    ______________________________________                                        Example DIA    STY    DVB  Tg   Shore D Hardness                                                                        DVB/STY                             ______________________________________                                        24      100    0      --   110  --        0                                     25 95 5 -- 112 -- 0                                                           26 85 15 -- 121 -- 0                                                          27 80 20 -- 124 -- 0                                                          28 90 10 -- -- 85 0                                                           29 90 10 2 -- 86 0.2                                                          30 90 10 4 -- 86 0.4                                                          31 90 10 6 -- 86-87 0.6                                                       32 90 10 10 -- 87 1.0                                                       ______________________________________                                    

EXAMPLES 33-39

These examples show that the styrene has an effective slowing down thephotochromic kinetics of the dyes in the copolymer matrix compared to amatrix formed from Diacryl 121 as the only monomer (Examples 33-37),that the divinyl-benzene has the opposite effect (Example 38), and thata mixture of styrene-divinylbenzene allows the adjustment of thekinetics to the desired value (Example 39).

In these examples, the polymerizable composition consisted of 0.2 partof AMBN, 0.4 part of DDT, 0.015 part of Sea Green dye and 0.30 part ofBerry Red dye, in addition to the monomers indicated in the table below,which also indicates the time for half-bleaching of the lenses obtained.

    ______________________________________                                                                   T 1/2 bleaching *                                    Example DIA STY DVB (in sec., 25° C., 560 nm) DVB/STY                ______________________________________                                        33     100    --      --   300          --                                      34 95 5 -- 330 0                                                              35 90 10 -- 460 0                                                             36 85 15 -- 550 0                                                             37 80 20 -- 630 0                                                             38 95 --  5 100 --                                                            39 80 11.7 7.3 330 0.62                                                     ______________________________________                                         * After an exposure time of 15 min. under the xenon lamp.                

The comparison of Examples 34 and 38 provides a good illustration of thecontrary effects of the two monomers, styrene and divinylbenzene, whichsuppress the optical distortions in the matrix.

EXAMPLES 40 and 41

These examples show that identical results can also be obtained by usingα-methylstyrene instead of styrene (Examples 40-41).

In these examples, the polymerizable composition consisted of 0.2 partof AMBN, 0.4 part of DDT, 0.015 part of Sea Green dye, and 0.30 part ofBerry Red dye, in addition to the monomers indicated in the table below,which also indicates the half-bleaching time of the lenses obtained.

    ______________________________________                                                                       T 1/2 bleaching (dry), (sec.)                    Example DIA ∝-Methylstyrene Tg 25° C., 560 nm                 ______________________________________                                        40     95     5           112  350                                              41 90 10 118 350                                                            ______________________________________                                    

We claim:
 1. Photochromic transparent organic materials presenting an index of refraction of more than 1.55, which are free of optical distortions, and prepared by radical polymerization of a polymerizable composition comprising:a) 80-95 wt % of at least one monomer represented by the general formula (I): ##STR11## where R=H or CH₃, and m and n are independently 1 or 2; b) 5-20 wt % of at least one aromatic monovinyl monomer represented by the general formula (II): ##STR12## c) an effective quantity of at least one dye that imparts photochromic properties to the material, selected from the group consisting of spiroxazines, spiropyrans and chromenes; d) an effective quantity of a linear alkanethiol chain transfer agent; and e) an effective quantity of a diazo compound as a radical polymerization initiator.
 2. Materials according to claim 1, wherein the polymerizable composition further comprises up to 10 wt % of an aromatic divinyl monomer represented by the general formula (III): ##STR13## R₁ =H or CH₃.
 3. Materials according to claim 2, wherein the ratio of the aromatic divinyl monomer to the aromatic monovinyl monomer is in the ratio of 0 to
 2. 4. Materials according to claim 3, wherein the aromatic monovinyl monomer is styrene.
 5. Materials according to claim 4, wherein the aromatic divinyl monomer is divinyl benzene, and the ratio of divinyl benzene to styrene is in the range of 0.2 to 1.0.
 6. Materials according to claim 1, wherein R=H, and m=n=2.
 7. Materials according to claim 1, characterized in that the chain transfer agent (d) is a C₄ -C₁₆ alkanethiol or a bismercaptoalkylether.
 8. Materials according to claim 7, characterized in that the chain transfer agent is selected from the group consisting of butanethiol, pentanethiol, hexanethiol, heptanethiol, octanethiol, decanethiol, dodecanethiol tetradecanethiol, and bis-mercaptoethyl ether.
 9. Materials according to claim 8, wherein the chain transfer agent is present in an amount in the range of 0.1-6.0 wt %.
 10. Materials according to claim 9, characterized in that the quantity of chain transfer agent is in the range of 100-5,000 ppm.
 11. Materials according to claim 1, characterized in that the radical polymerization initiator (e) is selected from the group consisting of azobisisobutyronitrile and 2,2'-azobis(2-methylbutyronitrile).
 12. Materials according to claim 2, characterized in that the aromatic divinyl monomer is divinylbenzene.
 13. Materials according to claim 1, wherein the polymerizable composition comprises a mixture of photochromic dyes, such mixture being capable of imparting a gray or brown tint to the materials in a darkened state.
 14. Materials according to claim 1, characterized in that the quantity of radical polymerization initiator is in the range of 0.05-0.5 wt. %.
 15. Method for the preparation of photochromic transparent organic materials having an index of refraction of at least 1.55, said method comprising radical polymerization of a polymerizable composition comprising:a) 80-95 wt % of at least one monomer represented by the general formula (I): ##STR14## where R=H or CH₃, and m and n are, independently, 1 or 2; b) 5-20 wt % of at least one aromatic monovinyl monomer represented by the general formula (II): ##STR15## R=H or CH₃ ; c) an effective quantity of at least one dye that imparts hotochromic properties to the material, selected from the soups of spiroxazines, spiropyrans, and chromenes; d) an effective quantity of a chain transfer agent; and e) an effective quantity of a radical polymerization initiator; provided that (1) the chain transfer agent is a linear alkanethiol chain transfer agent; (2) the radical polymerization initiator is a diazo radical polymerization initiator; or (3) the chain transfer agent is a linear alkanethiol chain transfer agent and the radical polymerization initiator is a diazo radical polymerization initiator.
 16. Method according to claim 15, wherein the polymerizable composition further comprises up to 10 wt. % of an aromatic divinyl monomer represented by the general formula (III): ##STR16## where R₁ =H or CH₃.
 17. Method according to claim 15, characterized in that the quantity of chain transfer agent is in the range of 100-5,000 ppm.
 18. Method according to claim 15, characterized in that the quantity of a radical polymerization initiator is in the range of 0.05-0.5 wt %.
 19. Photochromic article comprising a photochromic organic material according to claim
 1. 20. Photochromic article according to claim 19, wherein said article is an ophthalmic lens or a sun-protection lens. 